Loughner was charged with the attempted assassination of a member of Congress, two counts of killing an employee of the federal government, and two of attempting to kill a federal employee. There are expected to be further charges.

In a safe at his home the FBI found a handwritten note which said “I planned ahead” and “My assassination” along with the name “Giffords.” It was signed by Loughner.

In the safe they also found a letter to Loughner from Miss Gifford, thanking him for attending a similar “Congress on Your Corner” event in 2007.

Shot US congresswoman, Gabrielle Giffords is responding well to treatment but remains in critical condition after surgery, her doctors said.

Miss Giffords, 40, was shot in the head on Saturday at a public meeting in Tucson, Arizona. Six other people were killed in the attack.

Miss Giffords, a Democrat, was still alive on Sunday night despite a bullet passing through her brain.

The congresswoman was in a critical condition but doctors said she was able to communicate and follow simple commands such as raising one or two fingers or squeezing the hand of surgeons. She remained sedated and could not yet speak after a two-hour operation in which bone fragments were removed from her brain. Doctors said they were "cautiously optimistic."

A heroic woman who prised a magazine from the gunman as he tried to reload was credited with saving many lives.

Patricia Maisch successfully grabbed the gunman’s magazine as he tried to reload. He had already emptied one clip of 31 bullets. The gunman then tried to load a third magazine, but the spring in it failed and he was jumped on by two men.

Pima County Sheriff Clarence Dupnik said the “heroic” actions of the woman, who was not injured, had prevented an even “greater catastrophe.”

Mrs Maisch said she was “no hero.” She described how, after grabbing the magazine, she sat on the guman’s ankles while two people held him down.

She said: “I noticed that one of those people had a head wound so I called someone over and went to Safeway and got some paper towels. I thought about how lucky I was to be alive.”

Barack Obama called on Americans to observe a "moment of silence" at 4pm GMT on Monday.

"At 11:00 am eastern standard time (on Monday), I call on Americans to observe a moment of silence to honour the innocent victims of the senseless tragedy in Tucson, Arizona, including those still fighting for their lives," Mr Obama said in a White House statement.

"It will be a time for us to come together as a nation in prayer or reflection, keeping the victims and their families closely at heart."